Catalyst for the purification of exhaust gases of internal combustion engines

Abstract

A three-way catalyst is described for the purification of automobile exhaust gases formed of an active substance of platinum and rhodium and possibly base metal(s) at a certain weight ratio between the two noble metals and at a certain atomic ratio between the noble and the base metal, which are precipitated onto active aluminum oxide containing certain quantities of CeO 2 , ZrO 2 and Fe 2 O 3 , and whereby the catalyst is obtained by impregnating active aluminum oxide, possibly stabilized with alkaline earth metal, with a solution of cerium, zirconium and iron salt which is thereupon calcined in air at 500°-700° C. and then treated after application of an impregnation of salts of the active substance components in a gas current containing hydrogen at temperatures below 650° C.

What is claimed is: 
     
       1. A catalyst for simultaneous oxidation of carbon monoxide and hydrocarbons and reduction of nitric oxides in exhaust gases of internal combustion engines, comprising (a) 0.03-3% by weight of a platinum and rhodium containing active phase with a weight ratio between platinum and rhodium of 2:1-20:1;   (b) 5-15% by weight of a mixture of CeO 2  and ZrO 2 , whereby these oxides are at weight ratios of 20-80:80-20;   (c) 1-10% by weight of Fe 2  O 3  as well as   (d) a residual quantity up to 100% by weight of aluminum oxide of the transition series and obtained by impregnating a carrier material of Al 2  O 3  of the transition series, with an aqueous solution containing cerium, zirconium and iron salts or, mixing the carrier material with the respective oxides of cerium, zirconium and iron, tempering for 30-180 minutes in air at 500°-700° C. thereupon impregnating the carrier with an aqueous solution of a salt of platinum and a salt of rhodium, drying and subsequently treating in a gas current containing hydrogen at temperatures 250°-650° C.     
     
     
       2. A catalyst as defined in claim 1 wherein a coating comprising the components (a)-(d) is present on a honeycomb-shaped structural support made of ceramic or metal in a quantity of 5-30% by weight, related to the weight of the structural support. 
     
     
       3. A catalyst as defined in claim 1 wherein the carrier material is present in the form of molded bulk material. 
     
     
       4. A catalyst as defined in claim 1 wherein a coating comprising the components (a)-(d) is present on structurally reinforcing bulk material bodies of ceramic or of metal. 
     
     
       5. A catalyst for simultaneous oxidation of carbon monoxide and hydrocarbons and reduction of nitric oxides in exhaust gases of internal combustion engines, comprising (a) 0.03-3% by weight of a platinum, rhodium and at least one of the base metal elements aluminum, titanium, tin, chromium, manganese, cobalt and nickel containing active phase with a weight ratio between platinum and rhodium of 2:1-20:1 and an atomic ratio between the platinum group metals and the base metals which may be present of 1:6-2:1.   (b) 5-15% by weight of a mixture of CeO 2  and ZrO 2 , whereby these oxides are at weight ratios of 20-80:80-20;   (c) 1-10% by weight of Fe 2  O 3  as well as   (d) a residual quantity up to 100% by weight of aluminum oxide of the transition series and obtained by impregnating a carrier material of Al 2  O 3  of the transition series optionally lattice stabilized with an alkaline earth metal, with an aqueous solution containing cerium, zirconium, and iron salts or mixing the carrier material with a mixture of oxides of cerium, zirconium and iron, tempering for 30-180 minutes in air at 500°-700° C. thereupon impregnating the carrier with an aqueous solution of a salt platinum, rhodium and at least one base metal component, drying and subsequently treating in a gas current containing hydrogen at temperatures of 250°-650° C.   
     
     
       6. A catalyst as defined in claim 5, wherein the base metal is aluminum or nickel, and platinum group metals and aluminum or nickel are present in a weight ratio of 3:1-1:1 or 4:1-2:1. 
     
     
       7. A catalyst as defined in claims 5 and 6 wherein a coating comprising the components (a)-(d) is present on a honeycomb-shaped structural reinforcer made of ceramic or matal in a quantity of 5-30% by weight, related to the weight of the structural reinforcer. 
     
     
       8. A catalyst as defined in claims 5 or 6, wherein the carrier material is present in the form of molded bulk material. 
     
     
       9. A catalyst as defined in claims 5 or 6, wherein a coating comprising the components (a)-(d) is present on structurally reinforcing bulk material bodies of ceramic or of metal. 
     
     
       10. A process for the production of the catalyst as defined in claim 1 comprising impregnating a carrier material of Al 2  O 3  of the transition series, optionally lattice stabilized with an alkaline earth metal, with an aqueous solution comprising cerium, zirconium and iron salts or mixing with a mixture of their respective oxides, tempering for 30-180 minutes in air at 500°-700° C., thereupon impregnating the carrier with an aqueous solution comprising a salt of platinum, and rhodium thereafter drying the carrier and subsequently treating at temperatures of 250°-650° C. in a gas stream containing hydrogen. 
     
     
       11. A process as defined in claim 10, wherein the carrier material is tempered prior to impregnation with cerium- , zirconium- and iron salts or prior to the addition of the oxides of these elements, at 900° C. 
     
     
       12. A process as defined in claim 11 wherein the carrier material is saturated prior to tempering with an aqueous solution of an alkaline earth metal salt. 
     
     
       13. A process as defined in claims 10, wherein cerium nitrate, cerium acetate, ammonium cerium nitrate, cerium carbonate, cerium oxalate, cerium chloride or cerium citrate are used as the cerium salt; zirconium carbonate, zirconium acetate, zirconium nitrate, ammonium zirconium carbonate, zirconium oxychloride, zirconium formiate or zirconium propionate are used as the zirconium salt and in that iron formiate, iron nitrate, iron oxalate, iron thiocyanate, iron (II)-acetate, iron acetyl acetonate or ammonium iron citrate are used as iron salts. 
     
     
       14. A process for the production of the catalyst as defined in claim 5 comprising impregnating a carrier material of Al 2  O 3  of the transition series, optionally lattice stabilized with an alkaline earth metal, with an aqueous solution comprising cerium, zirconium and iron salts or mixing with a mixture of their respective oxides, tempering for 30-180 minutes in the air at 500°-700° C., thereupon impregnating the carrier with an aqueous solution comprising a salt of platinum, rhodium and at least one of the base metal elements aluminum, titanium, tin, chromium, manganese, cobalt and nickel, thereafter drying the carrier and subsequently treating at temperatures of 250°-650° C. in a gas stream containing hydrogen. 
     
     
       15. A process as defined in claim 14 wherein aluminum or nickel is used as a base metal and platinum group metals and aluminum or nickel are used in a weight ratio of 3:1-1:1, or 4:1-2:1. 
     
     
       16. A process as defined in claim 14 wherein the carrier material is tempered prior to impregnation with cerium- , zirconium- and iron salt or prior to the addition of oxides of these elements at 900° C. 
     
     
       17. A process as defined in claim 16 wherein the carrier material is saturated prior to tempering with the aqueous solution of an alkaline earth metal salt. 
     
     
       18. A process as defined in claim 14 wherein cerium nitrate, cerium acetate, ammonium cerium nitrate, cerium carbonate, cerium oxalate, cerium chloride or cerium citrate are used as the cerium salt; zirconium carbonate, zirconium acetate, zirconium nitrate, ammonium zirconium carbonate, zirconium oxychloride, zirconium formiate or zirconium propionate are used as the zirconium salt and in that iron formiate, iron nitrate, iron oxalate, iron thiocyanate, iron (II)-acetate, iron acetyl acetonate or ammonium iron citrate are used as iron salts. 
     
     
       19. A process for as defined in claim 10, wherein the carrier material is first applied on the honeycomb shaped structural support of ceramic or metal or on the structurally reinforcing bulk material bodies by bringing these in contact with an aqueous dispersion of the carrier material in solution, after removal of excess dispersion, drying, calcining at temperatures of 900° C. 
     
     
       20. A process as defined in claim 14 wherein the carrier material is first applied on the honeycomb shaped structural support of ceramic or metal or on the structurally reinforcing bulk material bodies by bringing these in contact with an aqueous dispersion of the carrier material in solution, after removal of excess dispersion, drying, calcining at temperatures of 900° C. 
     
     
       21. A process as defined in claim 10 wherein the structural support is brought into contact with an aqueous dispersion of aluminum oxide of the transition series containing the salts of cerium, zirconium and iron in solution or the oxides of these elements, removing the excess dispersion, drying and calcinining at temperatures of 500° C.-700° C. 
     
     
       22. A process as in claim 21, wherein alkaline earth metal-stabilized Al 2  O 3  is used. 
     
     
       23. A process as defined in claim 14 wherein the structural support is brought into contact with an aqueous dispersion of aluminum oxide of the transition series containing the salts of cerium, zirconium and iron in solution or the oxides of these elements, removing the excess dispersion, drying, calcining at temperatures of 500°-700° C. 
     
     
       24. A process as defined in claim 23 wherein alkaline earth metal-stabilized Al 2  O 3  is used. 
     
     
       25. A catalyst as defined in claim 5, wherein said alkaline earth metal is calcium. 
     
     
       26. A process as defined in claim 12 wherein the alkaline earth metal salt is a calcium salt. 
     
     
       27. A process as defined in claim 17 wherein the alkaline earth metal salt is a calcium salt.